The present invention relates to an electric power feeding device based on electromagnetic induction.
There has been known an electric power feeding technique in which a primary core having a primary winding and a secondary core having a secondary winding are coupled to form a magnetic circuit including gaps and power is fed from the primary winding to the secondary winding. The core structure is classified in terms of the shape of the primary and secondary cores into the channel-shape type (described in Japanese Patent Unexamined Publication No. 63-151006), the E-shape type (refer to FIG. 4), and the coaxial cylinder type (described in Japanese Patent Unexamined Publication No. 63-240331). The E-shape type and coaxial cylinder type cores are also called "three-leg cores" because of their three-leg cross section.
In the conventional power feeding device having the three-leg cores, the primary and secondary windings are wound on the respective primary and secondary copes having an E-shape cross section, and both cores are coupled for the transfer of power.
Since the three-leg, closed magnetic-path core has windings wound around a central column section, with outer column sections or a cylinder section covering the windings, it operates advantageously at little leakage of magnetic flux and therefore at high power conversion efficiency (the secondary effective power relative to the primary effective power) as compared with the channel-shape core (two-leg core)
However, in the application of the power feeding device to the electric automobile for example, there arise demands of increase in the power transfer capacity and decrease in the dimensions and weight, and it becomes necessary to raise the power frequency. It was recognized that a higher power frequency results in a larger magnetic resistance of the magnetic circuit including gaps and a significantly increased voltage drop due to the increased leakage flux.
The present invention is intended to deal with the foregoing prior art problem, and its prime object is to provide an electric power feeding device based on electromagnetic induction capable of drastically improving the power transfer efficiency.